My temp gauge, (thing with the water symbol) went super hot, and then back below 1/2 mark to cold. It keeps going back and forth, never past 1/2 way mark. Normal is at the 1/2 mark. What happened?

The ac fan only comes on when the ac is on , the engine fan comes on at engine operating temp . few things to check , the radiator core fins are free from rubbish leave or plastic bags , the thermostat is fully open , radiator tubes are blocked with gunk have it flow tested .

engine - Car temperature displaying below Cold or just ...

mechanics.stackexchange.com/.../car-temperature-displaying-below-cold...

Jun 25, 2012 - Today I was boiling inside my car as it was a very hot day and my ...cold, it almost never goes up to even 1/4 of the temperature gauge, the ... Where I live, it's hot enough that even with the thermostat wide open the engine won't stay at C.. ... How to Match Skin Color Between Pictures Of The Same Person In ...

What does it mean when my car's temperature gauge is halfway ...

https://answers.yahoo.com/question/index?qid...

Aug 23, 2011 - I think my temperature gauge is usually all the way to the left, which I think is "cold" (okay). ... before steam poured from under the hood of my car and I had to pay $217 ... Why does my A/C stop blowing cold & my temperature gauge goes toHOT? ... But the battery won't keep a charge after sitting over night. my temp gauge always stays on cold. never moves.? ' Yahoo Answers
Mar 28, 2014
My car temperature gauge started going crazy and it doesnt even ...
Nov 10, 2011
My engine temp gauge reads below normal, close to cold, even ...
Mar 23, 2007
my temperature gage on my car keeps going up and down.. does ...
Feb 15, 2007
More results from answers.yahoo.com

the first thing to check is to feel if the radiator is hot, if the radiator feels hot and the engine is also hot the coolant is circulating ok then the problem is more than likely electrical, the temp gauge gets its signal from the engine control module the coolant temp sensor sends coolant temp signal to engine control module for engine managment purposes then passes it to instument pack/gauge, if the sensor was at fault you would have engine running problems also,with poss fault codes logged, if the engine and rad are cold/only warm after the engine has been run for 15 mins or so it sounds like the thermostat is stuck open but you have changed that. i have had faulty new ones in the past and have had to test them in a pan of boiling water, hope this is some help to you.

The stepper motor that controls the gauge is bad , gm had problems with 03 to 06 vehicles . Here watch the video !

How to repair GM Instrument Cluster Speedometer Gauge Stepper

check your coolant level. It is important to pressure test the cooling system to ensure it can maintain 15psi pressure to keep the coolant from boiling off. When you accelerate combustion temperatures exceed 1000 degrees while the engine needs to operate between 190 and 220 degrees roughly. If your coolant level is good, replace your thermostat, which is usually cheap. If the problem persist you are looking at a possible water pump.

the first thing to try is turning the heater upto full heat(a/c off)if the temp guage goes down THEN CHANGE THE THERMOSTAT...(hot oil,if too hot, is thinner than the normal sae rating so the oil pressure will be lower.otherwise no real problem.

I really would like some clarification on that.
If your inside gauge seems to read cold for a while and then just goes hot it generally means either the gauge is sticking or much more likely the thermostat is sticking because it is about to go bad. Actually it has gone bad already if it is staying closed. Now most thermostats have a little bypass hole to let air and small amounts of water through to circulate all the time. this allows the hot water to actually reach the thermostat when it is mounted somewhat from the heat source. If that hole becomes plugged it will give the same effect since the entire engine has to get hot before the thermostat can even start opening. Once it starts opening it gets a rush of super hot water that slams it wide open.
If you don't notice any problems with the engine like water boiling over or any other strange behavior then it is likely the actual gauge in the dash sticking or the sensor malfunctioning.
What you want to do is take a laser temp gauge and get a temp reading off the radiator when the engine is reading hot. this will give you an idea whether or not it is lying to you. bring it over and ill lend you mine. ;)

first determine if the car is actualy getting hot.dont trust the gauge or fan for these are controled by a temp sensor, if the sensor went bad it will tell you its hot. the other thing it might be is a air bubble trapped in the system

change the thermostat and the temp gauge in the radiator

Hello there,

Either an air bubble, the thermostat or the water pump.

• Air bubble (pocket) - Just because the radiator is full, doesn't mean the engine is. When an air bubble circulates through an engine it will cause the temp gauge to swing from hot (when water is in contact with the sensor) to cold ( when air is in contact). The less water, the hotter the engine. Easiest fix - add water.
  
• Thermostat - Keeps water circulating in the engine separate from the water in the radiator until it gets to a certain temperature. At that point, it opens and allows the hot engine water and the cooler radiator water to cycle. Hot to radiator, cool to engine. As the cooler water flows over the thermostat, it closes, allowing the cycle to repeat. If it opens at the wrong temp, or not at all, your engine will overheat. Water will begin to boil. Steam will make the temp gauge swing erratically.
• Water pump - If the water pump is failing (sometimes the impeller will come of the shaft), the water will not circulate. Same results.
  

Troubleshoot:

• First and foremost: BE SAFE!!! Wear safety glasses. Start this with the engine cool. When you look in the radiator, do it from an angle and as far away as possible.
  
• Have a hose or a couple two liter bottles full of water.
  
• Take off the radiator cap. (Do not take off if engine is hot)
  
• Is the water level low? If so, top it off.
  
• Make sure the transmission is in either PARK or Neutral and set the parking brake.
• Start the engine.
• Observe the water level in the radiator. If it drops, top it off again.
  
• At first it should do nothing. The water in the engine is still cool. The thermostat is closed. As the water in the engine heats up, the thermostat will begin to open. When it does, you will notice the water level begin to surge up and down.
• Check your temp gauge. If the gauge getting close to the 'Red Zone', the thermostat should have begun cycling before now. Go back to the radiator and check it.
• When (if) the thermostat finally opens all the way, the water will start moving as it cycles through the system. You will be able to tell the difference.
• If you see the water flowing, the water pump is ok.
• If the water does not start to move and the gauge is getting close to 'Red', shut the engine down and let it cool. Do not put your face near the radiator. If the thermostat suddenly let go, The hot water, driven by steam, could erupt out of the filler hole. Replace thermostat. Rerun this test. If results are the same, replace water pump.
  
• Does the water level drop at this point (air bubble)? If so, top it off while it's circulating. Adding cold water will close the thermostat. Be prepared to wait through the cycling two or three times.
• Check the temp gauge again. Has it leveled off?
• When you don't need to add water any more, put the cap back on. Observe the temp gauge for a few more minutes. has it stopped the erratic behavior? If so, it was an air bubble and it's gone. If not, replace the thermostat.
  

Let me know how it goes. If you have any other problems, click the ASK button.

Remember: Good thing come to those who Rate.

Mike